Reactance control circuit



June 10, 1947. M. G. CROSBY 2,422,082

' REACTANCE CONTROL CIRCUIT Filed March 3, 1943 To DEMODULATOR JIGNHL SOURCE IFC DIJCRIMINHTOR- RECTIFIER LOG/9L OSCILLHT R X /.9 LEHST EFFECTIVE INVENTOR MURRAY 6. Cxeossr GRID I MP5 DANCE PLH 7:E V0]. 77965 ATTORNEY Patented June 10, 1947 2,422,0sa REACTA'NCE CONTROL omem'r Murray: G. Crosby-,- Riverhead; Ne Y aassimorgtor: Radio Gomoration of. Americai a corporationr ot-Delaware ApplicatiorrMarchs, 1943;";SeriaI-Noz entree My presentinventionrela'tes to reactance' control circuits; andLmOre particuIai-Iyto a method of; andmeans for, varying; the effective: magnitudeof' a reactance adapted" to be included in i an alternating-current. network;

It may-bestated tl'iat it is one of the main objectsm my-:present inventi'o-ntoprovide a'method of controlling the efiective magnitude of a reactance-by arranging the -reactance in series with the controI gridi-to-cathode space of an electron discharge tube; and varying the anode potential of the tube over a: relatively wide range of voltage:values-therebyto adjust the effectiveimpedance of the aforementioned? control grid-tocathode space;

Another: object ofmy: inventionis -to provide a: simple and'iefiective reactancecontrol circuit forregulating the frequenc characteristic of high frequency currentin'etworks, there being employed' 'as the reactance' control-circuit the series:

arrangement of a reactance' and the internal control grid to-cathode impedanceof a tube' whose anode potential? is varied over. a range of potentials to. provide adjustment of" the magnitude of the aforementioned iin-ternal :impedance;

Still other-objects of my: invention are to improve-, -enerall'ythe simplicityand eifi'ciency of reactancecontrol :lci-rcu-its; andcmore especially: to provide such circuits innan" economica1", manner.

Still other features: will best he understood:

by: reference :to the following description, taken in connection-:withather drawing; which I; have indicated diagrammatically several circuit. organizationsa wherebyrmyinvention may'be carried into efiect:

In the-drawing:

Fig: 1 shows a: generalized typeofacircuit to which-the: present. invention is-aapplicable;

Fig; 2 illustratesanembodiment:- of the; reactance control. circuit; I

Fig; 3::graphicallyrillustrates the functioning of the: circuit ofiFig: 2;:

Fig; 4= schematicallyshows; 3a superheterodyne receiver-to which the present: invention isapplied asan automatic frequency control (AFC);

Referringrnow' to the accompanying drawing, wherein like reference:- characters in the different figures: designatesimilar-circuit elements, in Fig.

1 I have showngthegenera'l type of network to which thepresent invention is applicable; In an osci-llatory circuit comprising an inductance coil land ashunt tuning condenser 2;, let it=loe assumedzthat' the circuit haste-predetermined :resonantfrequency: Assume; further; that the: cir- Quit lie-his; the tank; circuit-oi; the master oscillater: of a" frequency --mo.dulated's (FM) transmittert: To tvaryithefrequencysof circuit l--2 there issshunted :theiteacrosswa network compr s g g erally: a; .reasctance xlin series with a resisto R of adjustable-:magnitude.= The terminals 3" and '4 are. thei oppositesterminals Ofi'thB network' X-R. The reactance X-'may-he capacitative or induc tive. Varying the'tmag ni-tude ofiR will cause the reactance to varythe frequency. A' large magnitude of R'wi-lltcause theefiective magnitude of X to be small, whereas-:a small magnitude. ofR will permitta; largemagnitude ofrX to be-shunted across the-oscillatory-circuitz The resistive impedance R1 may be: provided by 4 an actual physical-resistor; or it may be provided by the plate resistance-nor "an electron discharge tube; The latter.=hasa-been employedlinthe past, but hasvarious:.disadvantages. According to'my presenttinvention; the; series: resistive impedance "R isprovid'ed :bya-an electronvdischarge device, but

itziis-ithe internal control grid to-cathode impede ance ofitheedevice.which-isutilized;

Referring touFigz' itrwilI-beseen that the reactance- X: is. capacitative; and: is"v designated" by reference-characterixa- Theeadjustableresistive impedance Rslis indicated? in: dotted" lines; since it iszthe internal resistive-impedance betweenzthe OGDtLOIJgEidiE? andcathodeafii of the electron. dis.- chargestuhe 1'3 Thetube 1: i SQS'hOWHaSY a triode byway-of example; any-desired 'type offtubecan tiesausedz. The: cathode rfii is. connected directly to ground-,,.or,' inlzgcnera'l toany point of relatively fixed alternating: potential; The control grid firiis returned:tongroundithrough the: inductance' coil? 8; Theiplate, or: anode; 9y of; tube 1 is: connected'zthrough. a; resistor; i0; which may have sis-magnitude ofaboutOfi megohm,-to adirect current voltagje source; The; anode 9"is connectedibmcondenserl I l-'toapoint:ofirelatively fixed-la ltematingpotential, such as ground; The condenser- H: may have: a: value: of about micro-micro-farads.

The direct;currentrpotential supply: source essentially provides a;wides-range'-ofpotentials, say between zero and:;minus-;22t5 volts tor -between .zero and; some: desired: positivevoltage. The direct current source for providing the 'control potentialstmay beeshuntedi bye: pctentiometeril 21 provided with a:sli'dabletapwl3 which isconnected in series-to resistor l-ll. Oiicourse; when the slider t3 issatvthezzerosor gIZOllnd';;p0iHt Of DDtEIItiOmBtEI' l:2-;,,the=;eleetroir.flolw from cathodei 6i to plate. 9 will, be greater: them-is: the: case :when the, slider [axis attthe mostneg-ative point-of potentiometer t2; inn-the:latteitcaseetnostEofitheseleetronsawould 7 AFC system accumulate in the space Accordingly, there would adjacent to cathode 6. be no significant flow of electrons through the control grid. In that case,

greatly reduced with plied to first detector 2| will be of a frequency to compensate for any shift inI. F. energy from a predetermined frequency value.

Where the tube I is used to provide frequency i modulation of carrier oscillations, themodulating signal voltage applied to plate 9 would be of audio frequency. The voltage, inthat case,

' wouldvaryove'r a Widerang'e pighegative and positive values relat'veto zero 10, the invention is not restricted to use of purely the result that the internal grid-to-cathode iin pedance would be low. be drawn toward grid That is, electrons would 5, and grid current flow would be had. In this case, "the efiective: series resistance in circuit with Xwouldhave less "value. It will, therefore, be seen that by varying the potential of plate 9 over a relatively widerange of negative voltage relatively simple method of varying magnitude of X0. One of the important advantages of this scheme is that'electron. flow may be provided in the control grid circuit of. tube 1- values there is provided a without space current flow through the plate circuit of the tube; Furthermore; thecontrol is sensitive, and, thereforeg'is of'value in the profrequency modulated oscillations; It determinedthat for duction of has been experimentally increasing magnitudes of -Xc,- theyfrequency deviation range will be greater. However, the constants of the. circuit will depend upon the use to which it is tobe put.

In Fig. 3 thereis presentedgraphically the relation between adjustment of the plate voltage of the electron discharge tube 1 and the grid impedance thereof. "It will be seen that when the plate voltage has maximum-negative value the grid impedance will be maximum, and, therefore, the seriesicapacitative-'reactance Xe will be ineffective. Onthe other hand, Xchas greatly increased eiiectiveness when zero value. It is to. be understood that [the graphical presentation of Fig-3 is'purely qualitative, and in no way restricts the scope of the invention. By increasingthe voltage "of the anode in a positive 'direction, and; above zero,

the value'of R can be further decreased.

In Fig. 4 I have shown in schematic form" an to which the invention may be applied. Those skilled in the art: arersofully acquainted with the dyne receiver that the latter is-schematically represented. There is schematically-shown a local oscillator 29 whose tunable tank circuit consists of the coil l and condenser 2. The local oscillations are fed to a first detector? 1 to which is also fed the received signal energy." 'The'usual I. F. (intermediate frequency) amplifier'ZZ is'fe'd from the firstdetector output; The 15F; output energy issupplied to a[discriminator-rectifier network 23, and the latter produces AFC voltage Which varies positive or negative'relative' to ground. I :1 The AFC voltage isutilized t'o'vary'the potential of plate 9, in the m anuer 'describ'ed in connection with Fig. 2. The output energy ofampli- 'fier 22 may also be used to feed a demodulator -or a second detector."-It is not believed necessary to describe the specific functioning of this application of'the invention; It is only necessary to point out that the-AFC circuit varies the potential of plate '9 in such a'manner that the inherent series resistance R has its rna'g'iiitride varied "so asto control the efiect of-Xe on the tankcircuit l-2.' Thefrequency of the-tarik :circuit is adjusted-so that the oscillations apthe plate voltage is networks of a superheterothe effective I value direct current voltage at the plate 9.

While I have indicated and described several invention is by no means limited to the particular organizations shown and described, but

that many modifications may be made without departing from the scope of my invention. What I claim is: 7

1. As a variable resistor element, an electronic device having'at least a cathode, control-gridland an anode, means establishing: the anode and cathode at ground potential for high frequency currents, means establishing the, grid and cathode at' a common point 'of'direct; current potential, terminals for utilizing theintern'al-gridi-tocathode impedance as ."solely a resistor element, a source of anode voltage and means'connecting said source to said anode foradjustingthe anode potential over a wide range, of voltagesthereby to vary said internal impedance in value;

2. In a device for varying the effective capacitative' magnitude of a condenser, atube provided With at least an electron emission electrode; a control grid and an anode, a source: of direct currentfor the anode; means connectingithegin ternal impedance between the grid" and emission electrode as a resistor element in series between said condenser and-ground; said grid and; emission electrode being at a substantially like-direct current potential, and "means for adjusting the anode over a wide range of directcurrentpotentials which are negative relative to ground; a

3. In combination with apairof: terminals between Which'exists a high ifrequencypotential, a series path between the terminals comprising a reactance and ares'istiv'e impedance of adjust- "device" provided with' at least "a control grid, cathode and auxiliary cold electrode, said resistive impedance consisting ofthe: internal controlgrid to cathode impedancebf said electron discharge device, said control grid being closer :to the cathode than said cold electrode, said grid. and

V cathode being at a substantia'lly'common direct current'voltage, a source ofcurrent'for said a uxiliary cold electrode, and:meansconnecting said cold electrode to 'said current so'urc'e fo'r' varying the potential-of said cold 'electrode over a "wide range of voltage va1uesthereby to:provide"ad justment of said resistive impedance over a relatively wide range for the'coritrol of "saidreactance'.

i l. In combination with apair "ofterminals between which exists a high frequency potential, a series path between the terminals consisting of a a condenser and a" control element therefore which consists of a'resistive" impedance bf adjut- J'able magnitude, an electron dischargedevice procloser to the cathode than sa'id plat vided with at leastfa"cathodefeontrol grid and plate, said resistive imped'ance'con's'istingof the "internal grid to" cathode impedance of said electron discharge device, said "control ridfbeing .f i ii voltage for' said plate, and means adjustably con- Hence, I

necting said plate to said voltage source for varying the potential of said plate over a wide range of voltage value thereby to provide a wide adjustment of said resistive impedance and a wide control of the value of said condenser.

5. In combination with a capacitative reactance, a resistive impedance connected in series relation with the reactance for controlling the efiective magnitude thereof, a triode provided with a cathode, control grid and plate, a source of plate voltage, said resistive impedance consisting of the internal control .grid to cathode impedance of said triode, said control grid being at a direct current potential substantially that of the cathode potential, and means connecting the triode plate to said source of potential for adjusting the plate potential over a wide range of values thereby to vary the magnitude of said resistive impedance widely.

6. In combination with a capacitative reactance, a resistive impedance in series relation with the reactance for controlling the efiective capacity magnitude thereof, a triode provided with a cathode, control grid and plate, said resistive impedance consisting of the internal control grid to cathode impedance of said triode, a source of direct current voltage for said triode, said control grid and cathode being at a common direct current potential, and means adjustably connecting said triode plate to said source of direct current potential for adjusting the plate potential over a Wide range of negative voltage values thereby widely to vary the value of the effective series resistive impedance.

7. A circuit for frequency modulating the oscillations of a resonant oscillation circuit, comprising a reactance, an electron tube provided with at least a cathode, control grid and anode, means for connecting in series across said oscillation circuit said reactance and the internal grid to cathode impedance of said tube, a source of modulating signal voltage, and means connecting said source to said tube anode for varying the anode potential over a range of negative and positive potentials thereby to adjust said internal impedance and consequently the effective magnitude of said reactance across said oscillation circuit.

8, Means for varying the effective magnitude of reactance in an alternating current network, said means comprising a reactance and an electron discharge device having a cathode, grid and an anode, means whereby said cathode and said grid are maintained at the same direct current potential, and means for adjusting the anode potential, the grid to cathode path of said device being in series with said reactance.

MURRAY G. CROSBY.

REFERENCES CITED The following references are of record in the file of this patent;

UNITED STATES PATENTS Number Name Date 2,231,367 Mountjoy Feb. 11, 1941 2,189,282 Foster Feb. 6, 1940 2,012,710 Crosby Aug. 27, 1935 2,294,100 Travis Aug. 25, 1942 2,153,779 Travis Apr. 11, 1939 2,058,411 Carlson Oct. 27, 1936 2,288,375 Townsend June 30, 1942 2,341,040 Hathaway Feb. 8, 1944 2,350,171 Lawrence May 30, 1944 2,361,634 Koch Oct. 31, 1944 2,361,731 Bach Got. 31, 1944 FOREIGN PATENTS Number Country Date 453,858 Great Britain Mar. 19, 1936 449,391 Great Britain June 15, 1936 492,408 Great Britain Sept. 20, 1938 495,339 Great Britain Nov. 11, 1938 OTHER REFERENCES The Use of Vacuum Tubes as Variable Impedance Elements, by Herbert J. Reich. Reprinted from Proceedings of the I. R. E., vol. 30, No. 6, June 1942, 250-40.6A. (Copy available for reference in Division 51.)

The Wireless Engineer, July, 1936, by Frank L. Hill, pages 370-373. (Copy available for reference in Division 51.)

Radio Engineering, by Terman, published by McGraw-Hill Book Company, Inc., New York, New York, 1937, p. 149. (Copy available for reference in Division 51.) 

